This invention relates generally to a control device of an automatic transmission for vehicles, and more particularly to a control device of an automatic transmission that provides learning control to enable completion of shifting in a predetermined period of time.
An automatic transmission changes gear positions by selectively actuating friction engagement elements such as clutches and brakes of a transmission gear mechanism by oil pressure. In this case, after the output of a shifting command, it takes much time to supply oil pressure to the selected friction engagement elements and the like, and thus, the start of the actual shifting in which the friction engagement elements start operating is delayed from a time indicated by the shifting command.
To change gear positions smoothly and quickly when controlling an automatic transmission, Japanese Laid-Open Patent Publication No. 1-193445, for example, proposes correcting an oil pressure in the next shifting based on the present shift time by learning control so that the actual shift time can be equal to a predetermined time.
Conventionally, to measure the shift time, a shift start determination gear ratio G1 is set in advance between a before-shifting gear ratio (the gear ratio of a before-shifting gear position) Gx and an after-shifting gear ratio (the gear ratio of a after-shifting gear position) Gy. A time point when the sequentially detected gear ratio crosses the shift start determination gear ratio G1 is regarded as a time point when the shifting is started, and a period of time until the gear ratio reaches a shift end determination gear ratio G3 set in the same manner as the gear ratio G1 is regarded as the shift time.
Incidentally, since the actual shifting starts when the gear ratio starts changing even at a low rate, the above-mentioned shift start determination gear ratio G1 is preferably set to a value as much close to the before-shifting gear ratio Gx as possible. Actually, however, the gear ratio G1 is set to a value smaller than the before-shifting gear ratio by a predetermined value in terms of dispersion in detection.
However, if the shift start determination gear ratio G1 is set to a value that is smaller than the before-shifting gear ratio Gx to a degree as mentioned above, the measured time is affected by a period of time until the gear ratio G1 is reached.
If, for example, an oil pressure in shifting is low and a change in gear ratio is extremely small at the start of shifting as indicated by xe2x80x9caxe2x80x9d in FIG. 6, there is a great difference between the actual shift time and the measured shift time. Even if the measured time is learned, it is impossible to properly correct an oil pressure in the next shifting.
More specifically, if it is determined that the measured shift time is shorter than a predetermined of time even though the actual shift time is longer than the predetermined period of time, the oil pressure is corrected to decrease in the next shifting. This may cause a shift shock.
On the other hand, if an engine races during shifting due to the unmatched engagement and disengagement.of the friction engagement elements as shown by xe2x80x9cbxe2x80x9d in FIG. 6, the same phenomenon occurs since it takes much time for the gear ratio to cross the shift start determination gear ratio.
As stated above, in the conventional way of measuring the shift time, it is impossible to measure the actual shift time, which is important in learning control, with desirable accuracy.
It is therefore an object of the present invention to provide a control device of an automatic transmission, which is capable of finding a shift time with high accuracy to provide proper learning control even in the case where a gear ratio changes at an extremely low rate at the start of shifting or in the case where an engine races.
To attain the above-mentioned object, according to the first aspect of the present invention, there is provided a control device of an automatic transmission, which selectively supplies hydraulic oil pressure to a plurality of friction engagement elements to change a plurality of gear positions by engaging and disengaging the friction engagement elements in combinations, the control device comprising: an oil pressure regulating actuator for regulating the hydraulic oil pressure; shift time learning control means for performing shift time learning control by comparing a target shift time and an actual shift time to thereby control the oil pressure regulating actuator; and wherein the shift time learning control means comprises gear ratio calculating means for finding a present gear ratio, and shift time measuring means for measuring the actual shift time by determining that shifting is started if the present gear ratio has repeated decreasing by a value equal to or larger than a predetermined unit gear ratio a predetermined number of times.
In the shift time learning control for controlling hydraulic oil pressure in the automatic transmission, since the actual shift time is measured by regarding as a shift starting point a time point when the present gear ratio has repeated decreasing by a value equal to or larger than a predetermined unit gear ratio a predetermined number of times, it is possible to surely detect the start of shifting without fail even when the shifting proceeds slowly due to a low hydraulic oil pressure. In particular, a smaller unit gear ratio enables the start of shifting to be detected earlier at a time point closer to the actual shift starting point. This improves the shift time measuring accuracy, and thus provides proper shift time learning control without causing a shift shock.
According to the second aspect of the present invention, the actual shift time is measured by regarding as a shift starting point an earlier time point between a time point when the present gear ratio has repeated decreasing by a value equal to or larger than a predetermined unit gear ratio a predetermined number of times and a time point when the present gear ratio reaches a first gear ratio that is set to a value smaller than a before-shifting gear ratio by a predetermined value.
By determining not only whether or not the present gear ratio has repeated decreasing by a value equal to or larger than a predetermined unit gear ratio a predetermined number of times but also whether or not the present gear ratio has reached the first gear ratio, it is possible to detect the start of shifting before the present gear ratio reaches the first gear ratio as a result of sequential decreases within the range of the unit gear ratio or more in the case where the shifting proceeds slowly, and it is possible to early detect the start of shifting since the present gear ratio quickly reaches the first gear ratio in the case where the shifting proceeds fast.
According to the third aspect of the present invention, the actual shift time is measured by regarding as a shift starting point a time point when the present gear ratio reaches a second gear ratio that is set to a value larger than a before-shifting gear ratio by a predetermined value.
In the case of shifting in which an engine races after the start of the actual shifting, it is possible to detect the racing of the engine if the present gear ratio has reached the second gear ratio and to detect the start of shifting at a time point in proximity to the actual shift starting point.
According to the fourth aspect of the present invention, the actual shift time is measured by regarding as a shift starting point an earlier time point between a time point when the present gear ratio reaches a first gear ratio that is set to a value smaller than a before-shifting gear ratio by a predetermined value and a time point when the present gear ratio reaches a second gear ratio that is set to a value larger than the before-shifting gear ratio by a predetermined value.
If the engine races during shifting, it is possible to detect the start of shifting when the present gear ratio reaches the second gear ratio, and if the engine never races during shifting, it is possible to detect the start of shifting when the present gear ratio reaches the first gear ratio. In either case, it is possible to early detect the start of shifting.
According to the fifth aspect of the present invention, the actual shift time is measured by regarding as a shift starting point the earliest time point among a time point when the present gear ratio has repeated decreasing by a value equal to or larger than a predetermined unit gear ratio a predetermined number of times, a time point when the present gear ratio reaches a first gear ratio that is set to a value smaller than a before-shifting gear ratio by a predetermined value, and a time point when the present gear ratio reaches a second gear ratio that is set to a value larger than the before-shifting gear ratio by a predetermined value.
Since the start of shifting can be detected if the present gear ratio has repeated decreasing by a value equal to or larger than a predetermined unit gear ratio a predetermined number of times or if the present gear ratio has reached the first or second gear ratio, it is possible to detect the start of shifting at a time point in proximity to the actual shift starting point irrespective of whether the shifting proceeds fast or not.
It should be noted that the above-mentioned unit gear ratio is preferably set to a value smaller than a difference between the before-shifting gear ratio and the first gear ratio.